We are investigating the structure and function of two iron proteins of the methylene hydroxylase of Pseudomonas putida, putidaredoxin and cytochrome P450 and of related proteins. The methods used involve Mossbauer spectroscopy, ESR and NMR. A number of spectrally different reaction intermediates of cytochrome P450 cam have been isolated that result from complex formation with substrate, putidaredoxin and O2. The changes in the electronic configuration and the geometry of the active center that take place as a consequence of these interactions can be studied very effectively by the spectroscopic tools we are using.